This invention pertains to a chemical-mechanical polishing system and method for polishing organic polymer films.
Compositions and methods for planarizing or polishing the surface of a substrate are well known in the art. Polishing compositions (also referred to as polishing slurries) typically contain an abrasive material in an aqueous solution and are applied to a surface by contacting the surface with a polishing pad saturated with the polishing composition. Typical abrasive materials include silicon dioxide, cerium oxide, aluminum oxide, zirconium oxide, and tin oxide. U.S. Pat. No. 5,527,423, for example, describes a method for chemically-mechanically polishing a metal layer by contacting the surface with a polishing composition comprising high purity fine metal oxide particles in an aqueous medium. Alternatively, the abrasive material may be incorporated into the polishing pad. U.S. Pat. No. 5,489,233 discloses the use of polishing pads having a surface texture or pattern, and U.S. Pat. No 5,958,794 discloses a fixed abrasive polishing pad.
Polishing compositions for silicon-based intermetal dielectric layers have been particularly well developed in the semiconductor industry and the chemical and mechanical nature of polishing and wear of the silicon-based dielectrics is reasonably well understood. One problem with the silicon-based dielectric materials, however, is that their dielectric constant is relatively high, being approximately 3.9 or higher, depending on factors such as residual moisture content. As a result, the capacitance between the conductive layers is also relatively high, which in turn limits the speed (frequency) at which the circuit can operate. Strategies being developed to reduce the capacitance include (1) incorporating metals with lower resistivity values (e.g., copper), and (2) providing electrical isolation with insulating materials having lower dielectric constants relative to silicon. Such low dielectric constant materials typically include organic polymer materials, inorganic and organic porous dielectric materials, and blended or composite organic and inorganic materials, which can be porous or non-porous. It would be highly desirable to incorporate low dielectric constant materials into semiconductor structures while still being able to utilize the conventional chemical-mechanical polishing (CMP) systems for polishing the surface of the resulting dielectric material during the semiconductor wafer processing.
Organic polymer materials typically have a dielectric constant value of about 3 or less. Organic polymer materials include polymers with a relatively high organic content, polymers with a low and high organic content with a high level of porosity, polymers with relatively low organic content based upon silicon-oxygen type materials and inorganic materials, or can be polymers with a combination of these properties. Such organic polymer dielectric materials have unique chemical and mechanical characteristics that must be addressed during chemical-mechanical polishing. Organic polymer materials generally are mechanically soft and readily exhibit plastic deformation, which makes them easy to scratch. In contrast to their mechanical sensitivity, however, organic polymers are often chemically inert. The combination of these chemical and mechanical characteristics makes organic polymer dielectric materials difficult to polish using a traditional aqueous based CMP system.
Several chemical-mechanical polishing systems have been used for the polishing of organic polymer materials. Neirynck et al. (Thin Solid Films, 290-291, 447-452 (1996)) discloses polishing compositions comprising alumina abrasive, either nitric acid or ammonium hydroxide, Triton-X, and optionally benzotriazole (BTA). Yang et al. (J. Electrochem. Soc., 144, 3249-3255 (1997)) discloses a polishing composition for benzocyclobutene (BCB) and parylene N (PA-N) films comprising nitric acid or ammonium hydroxide, alumina abrasive, optionally Triton-X, and water. Kuchenmeister et al. (Procedings of the Advanced Metallization Conference in 1998, 237-242 (November 1998)) discloses a CMP polishing composition for SiLK and BCB dielectric materials comprising alumina and an organic acid salt. Borst et al (Proceedings of the 4th International Conference on CMP Planarization (CMP-MIC), 409-412 (February 1999)) discloses CMP compositions for BCB and SiLK dielectric materials comprising alumina, water, nitric acid, organic surfactants, and optionally benzotriazole, and comprising alumina, water, and hydrogen peroxide. Borst et al. (J. Electrochem. Soc., 146, 4309 (1999)) discloses CMP compositions for BCB and SiLK dielectric materials comprising water, nitric acid, a surfactant, alumina abrasive, and hydrogen peroxide. U.S. Pat. No. 6,270,395 (Towery et al.) discloses a polishing composition comprising non-oxidizing abrasive particles in combination with a separate oxidizing agent, oxidizing particles alone, or reducible abrasive particles in combination with a compatible oxidizing agent.
A need remains, however, for a polishing system and polishing method that will exhibit desirable planarization efficiency, uniformity, and removal rate during the polishing and planarization of substrates containing organic polymer materials, while minimizing defectivity, such as surface imperfections and damage to underlying structures and topography during polishing and planarization. The invention provides such a polishing system and method. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
The invention provides a method for polishing a substrate comprising (i) providing a substrate comprising an organic polymer film, (ii) contacting the substrate with a chemical-mechanical polishing system comprising (a) a liquid carrier, (b) an abrasive and/or polishing pad, (c) a peroxy-type oxidizer, and (d) a metal compound with two or more oxidation states, wherein the metal compound is soluble in the liquid carrier, and (iii) abrading at least a portion of the substrate to polish the substrate.